A: The first step in this process is to differentiate the difference of a moisture barrier from a vapour barrier. To do this we start with understanding that water has three forms; 1) solid – ice 2) liquid 3) gas – vapour. We will be focusing on the liquid and gas/vapour forms to explain why you need a vapour not moisture barrier.
The term moisture barrier is commonly used to describe materials that will block water in its liquid form. Unfortunately this terminology is often misunderstood to also block water in its vapour form, which it does not. There are many materials that can block water in its liquid state but will allow vapour to pass freely. The most recognizable example of this is the textile, GORE-TEX®. “The secret of GORE-TEX® products -- which are both completely waterproof and completely breathable at the same time” www.gore-tex.com
This term is correctly used when the material will effectively inhibit the flow of water not only in its liquid form but also in its vapour state. This is crucial in flooring as many of the flooring materials can be greatly affected by water vapour which has caused numerous floors to fail. It is for this reason that building codes require vapour barriers and not moisture barriers.
The standard membrane for vapour barrier in building codes is 6 mil non-crossed linked polyethylene. So when you install our underlayments you are also installing the industry’s leading vapour barrier. Our underlayments start out as 36 mil cross linked polyolefin (blended) plastic, which give you a three pronged advantage:
1) We have incorporated polypropylene into the blending of the plastic because of its strength less porous properties then polyethylene.
2) Before our products go through the foaming process they are 36 mil (0.95 mm) which is 6 times the thickness of 6 mil poly (0.15 mm).
3) The cross linking process forces a tighter molecular connection of the cellular structure which increases its vapour protection.
It is through these technological advances that our underlayments are leading the flooring industry with a WVTR of .3 lbs/1,000ft2/24hrs.